An unusual dimagnesium-carbene complex could make a useful new catalyst, claim UK chemists.

A new tridentate ligand that tightly binds two magnesium ions has been developed by Polly Arnold of the University of Edinburgh and colleagues. The complex holds the magnesium ions in place through two N-heterocyclic carbene groups and a central amine, with the two metals sitting in the open face of the ligand where their reactivity can be exploited.

'N-heterocyclic carbenes are being explored intensively as ligands for homogeneous catalysts based on the soft, platinum group metals. We've been studying their binding to harder metal cations,' says Arnold. 'This new ligand is very straightforward to make - we hope that these complexes will show a very different type of catalytic activity to the softer metal-based systems.'

The Edinburgh team confirmed that the dimagnesium in the complex was accessible for reaction by substituting two chlorine ligands from the top face. The resulting structure formed colourless crystals from which x-ray structures could be obtained - revealing that the complex contains the shortest magnesium carbene bond ever seen.

Andreas Danopoulos studies carbene complexes at the University of Southampton, UK, and agrees that the magnesium structure could make a useful catalyst. But the complex could also be a source of new metal structures, he adds. 'The complex could be used further, using a transmetallation reaction to give transition metal carbene complexes, or even lanthanide or actinide structures.'

James Mitchell Crow